Shaping Solid-State Supramolecular Cavities: Chemically Induced Accordionlike Movement of gamma-Zirconium Phosphate Containing Polyethylenoxide Pillars

The hydrophilic oxygen atoms of polyethylenoxide chains inserted as pillars in gamma-zirconium phosphate form hydrogen bonds with the acid groups of the host. As a result the pillars are almost perpendicular to the gamma layers. Upon changing the pH level of the supernatant solution the hydrogen bonds are broken and the pillars become almost perpendicular to the layers (shown schematically). Thus there is a reversible enlargement-shortening of the interlayer space.     

Template evaporation method for controlling anatase nanocrystal size in ordered macroporous TiO2

The importance of pure-phase titanium oxide materials as catalysts, sensors, and photonic band-gap materials has been growing steadily. Recently, more attention has been focused on nanostructured titanium oxide showing controlled and periodic porosity on a nanometric scale. The nanocrystal size control of porous nanostructured titanium oxide in an anatase form is a crucial step for the organic template method. Simple template removal by evaporation in an inert atmosphere is reported in this article and compared with the calcination technique usually reported in the literature. The proposed method allows the formation of a double-porous (macro and meso) anatase phase. We demonstrate that it highly preserves the macropore order into a titanium oxide material and induces narrowly dispersed mesopores by controlling the nano-crystal size that is kept around 6 nm. For the proposed method, polystyrene beads are particularly suitable as templates, being evaporated in the temperature range of anatase existence. The final high surface area makes the materials appealing for applications as photocatalysts or sensors.     

Effects of Amine Oxide Surfactants on Reactions of Bromide and Hydroxide Ions with Methylnaphthalene-2-Sulfonate

The SN2 reaction of Br- with methylnaphthalene-2-sulfonate (MeONs) in water is accelerated by micelles of tetradecyldialkyl amine oxide (alkyl = methyl, n-propyl) and rates increase sharply in HBr due to increased binding of Br- to the protonated amine oxide. Second-order rate constants at the micellar surface are similar to those at surfaces of trialkylammonium and sulfobetaine micelles. The reaction of OH- with MeONs is weakly inhibited by amine oxide micelles, showing that dispersive, as well as coulombic and charge-dipole, forces play a major role in the association of ions with surfaces of micellar aggregates. Copyright 1999 Academic Press.     

A simple geometrical model for emulsifier free polymer colloid formation

In this paper we propose a simple model for the formation of monodisperse polymer colloids, which provides a convenient set of synthetic parameters for given bead diameters. We provide experimental data in support of this model.     

EQUILIBRIUM AMONG HEMATOPORPHYRIN DERIVATIVE COMPONENTSs—II. EFFECT OF ESTERASE ACTIVITY

Photofrin II is the hematoporphyrin-derivative fraction enriched in covalently-linked oligomers, characterized by a high degree of folding. Interaction with hydrophobic structures, such as biomolecules and cell structures, results in a modification of the equilibria among the different species, as a consequence of an unfolding effect exerted towards the electrostatic aggregates. The effect of esterase activity was evaluated, taking into account the nature suggested for the covalent linkage of the oligomers (ether and/or ester). The study was performed in Photofrin II aqueous solution by means of absorption and fluorescence spectral analysis. The results showed that the esterase is active only towards the unfold oligomers: that is, in Photofrin II solution supplemented with albumin. In these conditions, spectral analysis revealed the presence of a monomerization process, which is clearly evident during the first four hours of incubation. The monomerization effect induced by the enzyme was also proven by both equilibrium-dialysis measurements and zinc ion complexation. Zinc ion complexes with high affinity for monomeric species, giving rise to a very distinct emission band at 580 nm. The amount of ester linkage shown in the oligomers through enzyme hydrolysis appeared to be less than might have been expected, owing to the inhibiting effect of the monomer produced on the enzyme. The results are a step toward clarifying the intracellular and intratissue turnover of the drug observed after administration.     

Luminescence and anisotropy decays ofN-3-pyrene maleimide labeling IgG proteins and cells

The Py.M (N-3-Pyrene Maleimide) is a dye that covalently binds to reactive amino or sulfhycryl groups to give highly fluorescent protein conjugates. Measurements of luminescence lifetimes and anisotropy decays have been performed with a Phase and Modulation Fluorometer. Complexes of Py.M-antibody (IgG antimouse) and tumoral cells C6 labeled with Py.M have been investigated. The Py.M fluorescence in buffer solution and the protein and cells natural fluorescence have been checked. For Py.M-IgG and labeled cells, the fluorescence decays present interesting behaviours. The least-squares analysis of the experimental results on Py.M-IgG complex points out two lorentzian distributions centered at 74 ns and 11 ns, on the contrary, for the labeled cells, a discrete component at 100 ns and a lorentzian distribution centered at 5 ns are shown. In both systems a weak component lower than 1 ns is observed. The fluorescence decays, mainly the long lifetime one, are very sensitive to oxygen quenching, showing the high efficiency of O₂ quenching. For samples N₂ bubbled, the lifetime experimental resuits show a decrease of the oxygen accessibility from free probe in solution to Py.M-IgG complex and to labeled cells, compatible with a more compact packing of the probe binding site. The experimental results of anisotropy decays of degassed samples show for Py.M-IgG complexes a long rotation correlation time of about 200 ns at T=5°C, assigned to overall rotation of the protein, besides shorter correlation times attributable to inner protein motions. For labeled cells, the long rotation correlation time becomes of the order of 580 ns confirming a progressive increase of the stabilization of the binding site.     

Thermoanalytical and microscopical investigation of the microstructure of emulsions containing polymeric emulsifier

Polymeric emulsifiers provide exceptional stability to oil-in-water, water-in-oil or multiple emulsions by their steric stabilization. Pemulens as polymeric emulsifiers are able to stabilize o/w type emulsions because their short lipophilic part integrates into the oil droplets while their long hydrophilic part forms a micro gel around the droplet. In our present study the microstructure and integration of the polymeric emulsifier at the water-oil interface was investigated with thermogravimetric and microscopical methods. It was established that depending on the amount of both of the polymeric emulsifier and added coemulsifier the microstructure of the system changes.     

Field effect transistors with organic semiconductor layers assembled from aqueous colloidal nanocomposites

We demonstrate field effect transistors based on organic semiconductor molecules dispersed in a self-organized polystyrene (PS) latex bead matrix. An aqueous colloidal composite made of PS and tetrahexylsexithiophene (H4T6) is deposited with a micropipet into the channel of a bottom-contact field effect transistor. The beads self-organize into a network whose characteristic distances are governed by their packing. The semiconductor molecules crystallize in the interstitial voids, leading to the growth of large interconnected domains. Depending on the bead size and the ratio between H4T6 and PS, the fraction of the different phases in the polymorph can be controlled. In the transistors where the H4T6 metastable "red phase" is the largest, the device response and the charge mobility are comparable to those of sexithienyl thin films grown by high-vacuum sublimation.     

Presence of 137Cs, Pu isotopes and 241Am in ligurian and Tyrrhenian Seas sediments

During the last ten years, the Italian Universities of Parma and Urbino collaborated on a special radioecological program having the aim to study the levels and the distribution of long-lived radionuclides in different marine and terrestrial matrixes. This paper summarizes the results concerning the concentrations of ^239+240Pu and ²³⁸Pu, ²⁴¹Am and ¹³⁷Cs in sediments collected in the Ligurian and South Tyrrhenian Seas (Rapallo Harbour, Vado Ligure Canyon, Eolie Islands). Superficial sediments and sediment cores were collected. For cores the vertical distribution was calculated and the sedimentation rate obtained. ¹³⁷Cs was determined directly by gamma-spectrometry, while ^239+240Pu, ²³⁸Pu and ²⁴¹Am were separated by extraction chromatography, electroplating and determined by alpha-spectrometry. This revised version was published online in August 2006 with corrections to the Cover Date.     

Evolution of persistent Anthropogenic radioactivity in Antarctic ecosystems

The primary objective of this study was to observe the evolution of anthropogenic radioactivity contamination in the Antarctic continent throughout the period 1997–1999. Moreover, results have been compared with those obtained for previous expeditions, starting from 1987. As far as ¹³⁷Cs is concerned, interesting considerations could be made due to the great amount of available data. On the whole, radioactive contamination seems to be higher in continental than in marine environments. For lake algae, contamination seems to decrease gradually in the order: Tarn Flat, Edmondson Point, Carezza Lake. Focusing on ¹³⁷Cs activity data, a clear temporal decreasing trend was observed in all samples: for sea water, values decreased from mean values of 0.9?Bq/m³ in 1987 to 0.5?Bq/m³ in 1999, a 56% decrease (20% of the total is due to natural decay of ¹³⁷Cs). For lake waters and lake algae, the decreases are higher (80 and 30%, respectively) and the same can be assessed for sediments and soils, even if the resulting distributions are more complicated. The highest values for all radionuclides analysed were detected in terrestrial organisms (mosses, lake algae, and lichens). As a consequence, these matrices appear to be good bioindicators of radioactive contamination. Finally, although the Antarctic continent is affected by some degree by anthropogenic radioactive pollution, our results for ¹³⁷Cs show that we are facing a progressive decrease. Moreover, contamination in other parts of the world is much higher: from 6–10 times in the Mediterranean Sea and 20–50 times in the North Sea and Black Sea.